engleski

Serotonin (5HT) metabolism in the brain of Wistar-Zagreb 5HT rats

Introduction. Sublines of Wistar-Zagreb 5HT rats (WZ-5HT rats), characterized by constitutionally upregulated (high-5HT subline) or downregulated (low-5HT subline) platelet 5HT transporter (5HTT), display differences in the behavioural traits associated with 5HT neurotransmission, as well as differences in the 5HTT-related neuropharmacological response. On the other hand, no basal differences between the sublines were found in the expression and/or density of 5HTT and several 5HT receptors in selected brain regions. In attempt to characterise molecular mechanisms underlying observed changes in the brain functioning, here we have examined potential differences between 5HT sublines in the brain 5HT metabolism. Methods. Brain levels of 5HT and its major metabolite 5-hydroxyindoleacetic acid (5HIAA) were examined by HPLC-ED. Brain expression of 5HT synthesising enzyme tryptophan hydroxylase 2 (TPH-2) was assessed by western blot, real-time RT-PCR and in situ hybridisation. 5HT degrading enzymes monoamineoxidase A (MAO-A) and B (MAO-B) were analysed functionally by full kinetic measurement and at the level of mRNA by conventional RT-PCR. Results. Animals from high-5HT subline displayed non-significant trend towards reduction of 5HT and elevation of 5HIAA levels in multiple brain regions, resulting in a significantly higher (~10%, p<0.05) metabolic ratio (5HIAA/5HT) in the most regions examined. TPH-2 protein levels in the raphe nuclei region were for about 30% lower in high-5HT rats as compared to low-5HT rats, although the difference did not reach the level of statistical significance (p=0.1242). The same direction of changes, but also non-significant, was observed for TPH-2 mRNA levels, as assessed by real-time RT-PCR and in situ hybridisation. On the other hand, MAO-B mRNA levels in the cortical region were significantly (p<0.05), although slightly (~10%), increased in low- as compared to high-5HT subline, while no alternations were found in the raphe region. There were no differences between the sublines in the levels of MAO-A mRNA, as well as in the kinetic properties (Vmax, Km) of MAO-A and MAO-B isoenzymes, as measured in the whole brain homogenates. Conclusion. Results indicate that animals from the high-5HT subline have slightly increased brain 5HT turnover as compared to animals from low-5HT subline. In certain brain regions, indicated changes in the 5HT turnover could possibly be attributed to the alternations in the expression of 5HT metabolic enzymes.

serotonin; 5-hydroxyindoleacetic acid; monoamine oxidase; tryptophan hydroxylase; Wistar-Zagreb 5HT rat

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